Shaped articles of polyvinylidene fluoride

ABSTRACT

Vinylidene fluoride polymers having a crystallization temperature above 135*C and a melting temperature above 175*C. Articles such as fibers, films, etc., made from such polymers, have excellent heat-resistant properties and high mechanical strength. The aforementioned polymers may be produced by suspension polymerizing polyvinylidene fluoride in a water medium at a temperature preferably between 0*C and 30*C in the presence of a catalyst which may be a dialkyl peroxy dicarbonate or a dialkyl peroxy carbonate.

United States Patent Ishii et al.

SHAPED ARTICLES OF POLYVINYLIDENE FLUORIDE Hajime lshii; Nubuo Bannai; Sadao Nishita, all of lwaki, Japan Kureha Kagaku Kogyo Kabushiki Kaisha, Tokyo, Japan Filed: Sept. 22, 1972 Appl. No.: 291,694

Published under the Trial Voluntary Protest Program on January 28, 1975 as document no. B 291,694.

Related US. Application Data Division of Ser. No. 3,204, Jan. 15, 1970, Pat. No. 3,707,592, and a continuation-in-part of Ser, No.

501,888, Oct. 22, 1965, abandoned.

Inventors:

Assignee:

Foreign Application Priority Data Oct, 21, 1964 Japan 39-59812 Sept. 18, 1965 Japan 40-57016 US. Cl 260/92.l; 161/189; 264/210 R; 264/210 F; 264/235; 264/342 RE; 264/D1G. 73

Int. Cl. C08F 14/22 Field 01 Search 260/921 R Dec. 9, 1975 [56] References Cited UNTTED STATES PATENTS 2,435,537 2/1948 Ford et al. 260/921 R 3,012,021 12/1961 Hauptschein l R 3,031,437 4/1962 Iserson R 3,475,396 10/1969 McCain et al. l R 3,553,185 1/1971 Amagi et a1 260/92] R 3,574,178 4/1971 Toyoda et al. 260/92,] R 3,707,592 12/1972 lshii et a1 264/210 F Primary ExaminerJoseph L. Schofer Attorney, Agent, or Firm-Wenderoth, Lind & Ponack 57 ABSTRACT 3 Claims, 4 Drawing Figures US. Patent Dec. 9, 1975 Sheet 1 of2 3,925,339

FIG. 2

FILAMENT STRENGTH (g/Denier) N U h 01 O3 (P SHAPED ARTICLES OF POLYVINYLIDENE FLUORIDE REFERENCE TO RELATED APPLICATION This application is a division of application Ser. No. 3,204, filed .lan. l5, 1970, now U.S. Pat. No. 3,707,592, which in turn is a continuation-in-part of application Ser. No. 501,888, filed Oct. 22, 1965, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to improvements in the manufacture of polyvinylidene fluoride resins and formed articles of exceptionally high mechanical strength and resistance to heat and in the fabrication of polyvinylidene fluoride resinous materials through the melt extrusion process.

More particularly it relates to processes which include continuously extruding molten materials comprising linear polyvinylidene fluoride through an orificc, polyvinylidene fluoride resins capable of being obtained by polymerization at a relatively low temperature, and to improved mouldings having an excellent processability and heat resistivity.

SUMMARY OF THE INVENTION The first object of this invention is to provide polyvinylidene fluoride mouldings having heat-resistivity extremely higher than the conventional polyvinylidene fluoride, high mechanical strength at a high temperature, and excellent dimensional stability.

The second object of this invention is to provide polyvinylidene fluoride mouldings of exceptionally high resistance to heat, the melting temperatures of which are higher than 175C and the crystallization temperatures of which are higher than 135C.

The third object is to provide preferential polyvinylidene fluoride resinous materials for melt extrusions, which can be easily extruded with exceptionally low melt viscosities, and the inherent viscosity (to be defined hereinafter) which is below 1.20 and above 0.40.

The fourth object is to provide polyvinylidene fluoride mouldings through melt extrusion and injection without or with any plasticizers (less than 5 percent which are more resistant to heat than well-known commercial polyvinylidene fluoride mouldings and have good mechanical properties.

The fifth object is to provide improvements in manufacturing polyvinylidene fluoride fibre or film, the tensile strength of which is substantially high. These improvements include processes which comprise continuously extruding the molten materials consisting of linear polyvinylidene fluoride without a plasticizer through a spinneret or a slot orifice, stretches and anneals.

A more specific object is to provide a method for producing low denier, high tenacity, textile and industrial filaments or thin and tough films from the molten linear polyvinylidene fluoride with a minimum of meltextruding apparatus.

These and other objects will become more clearly apparent hereinafter, and the nature of the present invention will be described in the following with respect to principles and typical examples of the procedure and results.

BRIEF EXPLANATION OF DRAWINGS In the accompanying drawings:

FIGS. 1(a), 1(b), and He) are, respectively, X-ray diffraction pattern photographs (in the case where the value of (l /l is greater than 1.3) of a polyvinylidene fibrous formed articles having, principally, an a type crystalline structure, X-ray diffraction pattern photo graph (in the case where (I ,/l 2 is about 1.3) ofa polyvinylidene fibrous formed article having a crystalline structure at least one part of which has been transformed to B type crystalline structure, and X-ray diffraction pattern photograph (in the case where (1 /1 is about 0.0) of a polyvinylidene fibrous formed article having, almost completely, B type crystalline structure.

FIG. 2 is a graphical representation indicating the relationship between the intensity ratio (l /I in the X-ray diffraction diagrams of various fibres obtained by various conditions of stretching and the tensile strength of these fibres, said fibres having been, obtained by subjecting a polyvinylidene fluoride resin having inherent viscosity 1; inh of 0.92 to melt-spinning.

DETAILED DESCRIPTION OF THE INVENTION Applicants have found that the polyvinylidene fluoride of the present invention has a melting temperature of above at least about 175C and a crystallization temperature of about 140C, which were both comparatively higher than that of the known polyvinylidene fluoride prepared at a higher temperature, when vinylidene fluoride monomer was polymerized at 0 to 60C, particularly 40C, by some peroxide catalysts such as dipropylperoxydicarbonates. Therefore, the resistance to heat of the polyvinylidene fluoride mouldings of this invention, provided through the processes such as meltextrusion and injection, has been at least 10C higher than that of the well known polyvinylidene fluoride mouldings.

Furthermore, we have found that, in the case of said polymerization, the polyvinylidene fluoride the polymerization degree of which has been adjusted so that inherent viscosity of the polymer becomes 0.4 1.2 has, although crystallization temperature and melting point of said polymer are relatively high, such a very low melt viscosity at a processing temperature and such an excellent processability as enabling very easy production of an excellent formed article having high heatresistivity and mechanical properties.

For example, in the case of a polyvinylidene fluoride obtained by polymerizing vinylidenefluoride at a temperature between 20 and 30C in the presence of a chain transfer agent and diisopropylperoxydicarbonate catalyst and having an inherent viscosity of 0.94, melting point and crystallization temperature were higher, by about 15C, than those of the conventional known polyvinylidene fluoride, but apparent viscosity in the case of extrusion at a temperature of 250C and a pressure of kg/cm was 9,000 poise. Furthermore, melt of said polymer resin had an excellent drawability. Heat-deformation temperature of the article formed from the abovementioned resin was 164C (or C) at 66 psi (or 264 psi) according to ASTM-D648, said temperatures being higher (by about 15 30C), respectively, than those of the conventional known polyvinylidene fluoride.

Of course, there is a clear relationship between the inherent viscosity and melt viscosity of any polymer. In general, when the inherent viscosity decreases, the melt temperature decreases, but crystallizability of the polymer becomes high, whereby it is presumed that melt viscosity increases with increase in the crystallization temperature.

It is surprising that melt viscosity of the polyvinylidene fluoride obtained by low temperature polymerization is very low in spite of the fact that melting temperature and crystallization temperature of said fluoride is higher such as by about 15C.

Since there is an intimate relationship between the inherent viscosity and polymerization degree of the polymer, when said viscosity is decreased, the mechanical properties of the polymer become inferior. How ever, mechanical strength of the formed article produced by use of a vinylidene fluoride having an inherent viscosity of 0.94 is not inferior or more excellent than that of the conventional known polyvinylidene fluoride. This point is a characteristic feature of the instant polyvinylidene fluoride prepared by suspensionpolymerization at such low temperature.

The formed article made of polyvinylidene fluoride of this invention is obtained by suspension polymerizing vinylidenefluoride at a temperature between l and 60C, preferably between 0 and 40C so as to obtain polyvinylidene fluoride having a melting point about 180 190C, and subjecting said product to extrusion with or without addition of a plasticizer percent by weight).

A feature of the polymerization applied in the invention may be represented as follows:

The polymerization catalyst having a half life time of less than I00 hours at 50C has been preferred especially for the polymerization of vinylidene fluoride such as that by the suspension technique. it has been desired that these catalysts do not immediately terminate the polymerization reaction during the initial period. The hydrogen atom of the catalysts may be easily extracted by the environmental vinylidene fluoride radical, because the vinylidene fluoride radical has a strong affinity to the hydrogen atoms and the extracted hydrogen atoms become the polymerization stoppers or the chain transfer agents.

Therefore, it may be said that the applicable catalysts are enumerated as follows:

I It l-Q-C-O-O-C-O-H where R is a primary alkyl group of C l 4 or a secondary alkyl group of C 3 6, or

where R is a primary alkyl group of C l 3, a secondary alkyl group of C 3 5, and/or a tertiary alkyl group of C 4 6, and R is a primary alkyl group of C l 3 or a secondary alkyl group of C 3 5.

Of the dialkylperoxydicarbonates, there may be mentioned such compounds as diisopropylperoxydicarbonate, disecondarybutylperoxydicarbonate, di-secondaryamylperoxydicarbonate, disecondaryhexylperoxydicarbonate, diethylperoxydicarbonate, di-n-propylperoxydicarbonate, and di-n-butylperoxydicarbonate.

In respect to the diall-tylperoxycarbonates, there may be mentioned such compounds as wherein the R groups are methyl, ethyl, n-propyl, isopropyl, secondarybutyl, 2-methyl butyl, tertiary butyl, tertiary amyl and 2,2-

dimethyl-butyl, and wherein the R' groups are methyl, ethyl, n-propyl, isopropyl, secondarybutyl and secondary amyl.

However, in these catalysts also, a hydrogen extracting action caused by vinylidene fluoride-radical is achieved, so that the catalysts themselves function as polymerization degree controlling agents and the inherent viscosity of the polymer can be easily controlled by controlling the quantities of the catalysts and polymerization temperatures.

On the other hand, since it is usual to use an expensive catalyst as the polymerization degree controlling agent and use of a large quantity of said catalyst causes reduction of the heat-stability of the produced polymer, it is preferable to control the polymerization degree by using a chain transfer agent. As such chain transfer agents, for example, well-known chain transfer agents such as chloroform, carbon tetrachloride, trichlorethane, n-hexane, cyclohexane, etc. can be used.

Among said radical catalysts, the catalyst having a short period of half decay, containing hard transferable hydrogen in its alkyl-radical, and capable of being handled in a relatively safe manner is mostly preferable. As these catalysts, there are diisopropyl peroxydicarbonate and ditertiary butylperoxydicarbonate, but the diisopropyl peroxydicarbonate is the most excellent one.

The polyvinylidene fluoride resinous materials polymerized at 0 to 60C, especially at 40C, by using the abovementioned agents, are crystallizable, the melting temperatures of which were higher than 175C and the crystallizing temperatures of which were higher than C. Furthermore, the resistance to heat of the abovementioned polyvinylidene fluoride is improved markedly.

Furthermore, the polyvinylidene fluorides resinous materials having easy processability with especially low melt viscosity through processes such as melt extrusion and injection, have been obtained by the abovementioned polymerization, where the degree of polymerization of the polyvinylidene fluoride was eliminated that is to say the inherent viscosity was eliminated to 1.20 from 0.40. Further features of the present invention are mentioned with respect to the following examples.

PREFERRED EXAMPLES OF INVENTION EXAMPLE 1 Suitable polyvinylidene fluoride powders for the purpose of this invention may be made by suspension polymerization techniques using the following recipe:

vinylidene fluoride 1200 g methylcellulose 3.6 3 water 3600 g The reaction is carried out with stirring at a rate of 300-350 r.p.m. under the conditions of variable amounts of isopropylperoxydicarbonate and chloroform added. The various polymerization conditions are shown in Table l.

The expression inherent viscosity denoted by the symbol 1 inh is used as a measure of the degree of polymerization of the polyvinylidene fluoride and may be defined as:

ninh (ln 'nr/C) (Where 1 is the relative viscosity of a dilute dimethylformamide solution of the polyvinylidene fluoride divided by the viscosity of the dimethylformamide per se measured in the same unit at the same temperature (30C), and C is the concentration in grams of the polyvinylidene fluoride per 100 cc of solution (0.4g in this invention).)

(Table lI)-continued Physical Properties of Various Polyvinylidene Fluoride Resinous Materials Crystalli- Kind of Melting zation" Specific polyvinylidene ninh temperature temp. gravity fluoride (peak) (peak) Measured with a Shimadzu DT-lO type differential thermal analyzer at a rate of temperature rise of 10Irnin. "Measured with the same apparatus at a rate of temperature fall of 8C/min,

Percentages are by weight with respect to monomer.

EXAMPLE 2 It has been found that there are clear differences in physical properties between the polyvinylidene fluoride of this invention which is indicated in Table I and the commerical polyvinylidene fluoride. For both polyvinylidene fluoride resinous materials, Table II shows 1 inh, melting temperature and crystallization temperature measured by differential thermal analysis. and specific gravity, respectively. As shown in Table 11, it has been found that the melting temperatures of the polyvinylidene fluoride of this invention is about C higher than that of the known commercial polyvinylidene fluoride, while 1; inh or the degree of polyme r ization of the former was comparatively lower than that of the latter. Moreover, the differential thermal analysis curves show that the endo-therms of the polyvinylidene fluorides of this invention are sharper and much more than those of the known commercial polyvinylidene fluorides when measured in the case of rising temperature. The crystallization temperature of the polyvinylidene fluoride of this invention was also about 15 20C higher, the exo-therms were sharper and much more than those of the known commercial polyvinylidene fluorides when measured in the case of falling temperature from above their melting temperatures.

(Table ll) Physical Properties of Various Polyvinylidene Fluoride Resinous Materials It is thought that the differences of the melting temperatures and crystallization temperatures suggest some inherent differences of molecular structure comprising between the polymeric materials of this invention and the known commercial polymeric materials and that the degree of crystallinity of the polyvinylidene fluoride of this invention may be somewhat higher than that of the commercial polyvinylidene fluoride, as shown in Table II, in which the specific gravity of the former was higher than that of the latter.

EXAMPLE 3 From the above-described Example 2, it may be concluded that the resistance to heat of the polyvinylidene fluoride of this invention is superior to that of the well known polyvinylidene fluorides. The measurements of the deflection temperatures by the ASTM method revealed more clearly the superiority of the polyvinylidene fluoride of this invention, as shown in Table III.

In this table, the specimens of the polyvinylidene fluorides were made from compression mouldings, and the loads used for measuring were 66 and 264 psi.

(Table 111) Thermal Deflection Temperature kinds of thermal deflection temperature C polyvinylidene 66 psi 264 psi fluoride this invention A 165 120 B 165 120 C l known commercial A further feature of the present invention is the provision of preferable polyvinylidene fluoride resinous materials for the purpose of melt extruding. It may be said that the degree of polymerization or 1; inh of the polymeric materials is very important in melt extrud ing, and it is preferable to select 17 inh as low as possible in order to obtain easy processability, although the decrease in 'q inh lowers to some extent the physical properties of the polymeric material mouldings. Accordingly, the easy processability for the melt extruding the polyvinylidene fluoride of this invention corresponded to 'q inh, which is closely related to the apparent melt viscosity.

In this invention, the purpose for providing the preferable polyvinylidene fluoride resinous materials polymerized at to 60C, particularly 40C, has been essential for the production of fibre or film through a thin orifice as well as for decreasing melt viscosity. For industrial production of low denier filaments, it should be said that the apparent melt viscosity was as low as at least about ten thousand poise, because the higher poise was too viscous to flow forming itself into a filament with the smooth and gloss surface through a fine orifice. Therefore, it has been necessary to eliminate 17 inh of the polyvinylidene fluoride of this invention within 1.20 in order to obtain the apparent melt viscosity below about ten thousand poises. Moreover, we have unexpectedly found that the polyvinylidene fluoride fibre made from the lower inherent viscosity had stronger tensile strength than that of the higher inherent viscosity of which apparent melt viscosity was as high as beyond about 10,000 poise. According to further feature of the present invention, there was a maximum peak of the tensile strength at the polyvinylidene fluoride fibre of 1 inh about 0.90 0.95, the melt viscosity of which was of medium value of about 5,000 poise.

A fibre of film of linear high polymer comprising vinylidene fluoride has been known by US. Pat. No. 2,435,537, which revealed the tensile strength of a polyvinylidene fluoride film to be 3.7 kg/mm and was recently reported by Pennsalt Chemicals Corporation Bulletin UF2R-62 to be 3.5 4.0 g/D strength of a polyvinylidene fluoride filament, the production process of which was a casting method using polyvinylidene fluoride dispersions, which is more expensive than the melt extrusion process.

We have found that the polyvinylidene fluoride resinous materials polymerized at 0 to 40C, 1 inh of which was below 1.20, particularly 0.95, were easily melt extruded at nearly 250C through a fine spinneret, wound up at a very high speed, and stretched thereafter immediately or soon by a draw ratio of at least 150 percent, particularly 300 percent, before heat-setting.

In melt spinning, the wind-up linear velocity or draft ratio 2, which is herein defined as the ratio of wind-up linear velocity to exit linear velocity at orifice, is very important when producing continuously uniform lowdenier and high-tenacity filament. It may be said that excellent filament of polyvinylidene fluoride has been made from a melt extrusion the draft ratio Z of which is more than about ten. In the melt-spinning of polyvinylidene fluoride resinous materials, the value of n inh of which was larger than 1.20, the extruded filaments could not be wound up subsequently even at a moder ate draft ratio of more than about ten times. Furthermore, these filaments were hardly oriented along the stretched direction. Consequently, the tensile strength of these filaments, the 1; inh of which was higher than 1.20, was not improved well enough. The melt spinning of commercial polyvinylidene fluorides, the 1 inh of which was about 1.4 to 1.9, was also difficult.

In order to indicate the specific flow properties and fibre forming properties of the various polyvinylidene fluorides resinous materials, the apparent melt viscosities of the various polyvinylidene fluorides are shown in Table IV, and the draft ratios in the melt spinning are shown in Table V corresponding to Table IV.

In Table [V and Table V, the apparent melt viscosities and the draft ratios, respectively, in the cases of two different extruding temperatures of 250 and 280C and different extruding pressures of 100, 200 and 300 ltg/cm are shown, in the case of experiments on known commercial polyvinylidene fluorides, the draft ratios being less than 10, despite the apparent melt viscosity of less than 10,000 poises at 300 kg/cm'. Therefore, the excellent fibre forming properties may correspond to lower melt viscosity accompanying higher draft ratio at lower extruding pressure and lower extruding temperature above the melting point. From these results, it is apparent that the melt extrusions obtained from the examples 1, 2 and 3 of this invention had the most preferential fibre forming properties which produced excellent high-tenacity filaments.

Of course, melt extrusions, which had very low melt viscosity accompanying the large draft ratio, have been obtained from polyvinylidene fluoride of 1 inh below 0.40, but the finished filaments made from these extrusions were weak and unpractical.

Another feature of the present invention relates to cold or thermal stretching, from which superhightenacity polyvinylidene fluoride fibre is resulted.

As a result of X-ray diffraction investigations of the polyvinylidene fluoride, mouldings through an orifice or the unstretched fibre obtained by the melt extrusion, an unoriented a-type X-ray diagram together with a faint 'n-type X-ray diagram were obtained. It may be defined in this invention that the a-type diagram shows a quadruplet diffraction (I at 3.24 A and a fi-type diffraction shows a quadruplet diffraction (1 at 2.16A. When an unoriented fibre or film is stretched to some extent of draw ratio and heatset, the X-ray diagram shows an oriented fibre diagram which is a mixture of a and B type diagrams.

(Table IV) Apparent Melt-Viscosities of Various Polyvinylidene Fluorides (Table lV)-continued Apparent Melt-Viscosities of Various Polyvinylidene Fluorides Kind of poly- Apparent melt viscosity (X l0 poise) vinylidene 250C 280C fluoride 100 200 300 100 200 300 ltg/cm leg/cm kg/cm kg/cm kg/cm k /cm known commercial In 200 39 16 100 24 1t Measured by using a Shimadzu type (Koltzrtype) Flow Tester with an orifice of 0.5 mm diameter and mm length.

We have found that the intensity ratio l,/l is closely related to the tensile strength of the polyvinylidene fluoride fibre.

FIG. 2 shows the relationship between the intensity (Table ratio l,/lin the X-ray diffraction diagrams of various Rams and Fibre Fmmmg propcmes 25 fibres obtained by various conditions of stretching and f Vari us P lyvinylidene Fluorides the tensile strength of these filaments. g'gj f 250C Draflram 280C Each of the samples used in the photographing of vhwhdene 100 300 m0 300 said X-ray diffraction photographs was formed to be a fluoride g/ og/ ug/cm kg/cm fibre bundle having a dimension of 0.5 mm X 5 mm and this photographing was carried out by use of an electric invention power of 40 kV X 20 mA, Ni filter, and a slit of 1 mm. 150-200 50400 g gag than The distance between the sample and camera was 40 8 100-150 100-150 more than more than mm. In the measuring of (1 /1 a sample having a 200 200 dimension of0.5 X 5 X 20 mm which was formed by use C r b d1 f f'b r 0.06 and collodion solution D less than less than less than less than 0 a un e 0 l res 0 g i 2 s s 10, rough was subjected to a measuring by use of a Geiger Surface Surface surface counter, a Ni filter, a slit of l mm, and an electric known power of 40 kV X 20 mA. In this invention, thermal com'qercial than than than stretching operation can be carried out at a temperarough n mmugh 40 ture between room temperature and 175 C, but it 15 surface preferable to carry out the stretching at a temperature H 5 33; f6? $22,, 52332,, between 80 and 130C and then to carry out secondsurface surface surface surface ary stretching and or heat setting at a temperature m 5 :32,? f5? $32,, f ggg between 1 30 and 175C. In this case, it is preferable to surface surface surface surface carry out the primary SIICIClImg at a stretching rate The unoriented polyvinylidene fluoride fibre could be stretched to about 4 times the draw ratio at room temperature or above, but it has been desirable to stretch at a temperature above room temperature up to 175C, particularly 130C.

Unexpectedly, the X-ray diffraction diagrams the intensity of 1,, the quadruplet diffrection of a-type is weaker. and the intensity of 1 the quadruplet diffraction of B type, is stronger in the case of higher draw ratio of the stretching. l, vanishes, and there is strong 1 only when the orientation effect on the stretching has become very large. The intensity ratio I,/l is closely related to the draw temperature and the drawing technique, as well as the draw ratio of the stretching, For instance, l,/l is less (degree of change from a to ,8 has been great) when the draw temperature is low. l,/I is zero when the first stretching is carried out at 80 130C, and subsequently the second stretching is car ried out at 80- 175C, while l,/l is not zero even ifthe draw ratio is the maximum, when only one stretching was carried out at a temperature higher than 130C.

above 150 percent and further improvement of (|,/l,) and strength of the product can be attained by carrying out the secondary stretching at a stretching ratio of above 5 percent. The properties of the filaments which were sujected to stretching operation as described above are shown in Table VI.

The table Vl relates to test of filaments obtained by subjecting polyvinylidene fluoride resins to spinning operation through a nozzle of 0.5 mm CD, said resins having been produced by the substantially same process as the polymerization examples 1, 2 and 3 and having 1 inh of 0.84, 0.92 and 1.06 respectively, and by winding up said filaments at a draft ratio such as indicated in said table. These filaments were subjected, after primary stretching thereof at C, to heat setting for 1 hour at a temperature of 120C and stretching ratio of 2 percent. Then, these stretched filaments were, after secondary stretching of 20 percent at C, subjected to heat setting for one hour at C. (1,0 strength and stretching ratio of said filaments were compared in the Table V1 with those of the filaments made of the conventional polyvinylidene fluoride.

Table VI PROPERTIES OF STRETCHED FILAMENTS MADE OF POLYVINYLIDENE FLUORIDE Polyvinylidene Fluoride of this Invention Inherent Draft Primary stretching Heat Secondary stretching Heat IJI, Strength Extension viscosity ratio temperastretching setting tempera stretching setting g/ Denier ture ratio temperature ture ratio temperature do. 120 I20 300 150 1/2 6.0 22 do. 120 I20 400 150 1/4.5 6.5 20 dov I20 I20 400 I50 I50 20 I70 011 7.0 20 I06 25 120 300 150 III 5.5 25 do. 25 120 300 150 150 20 170 /1 6.5 20 Known Commercial 1.4 Draft is 140 300 2/1 2.5 25

impossible 1.6 Draft is 120 Impossible 4/l impossible do. 140 300 2/] 2 25 In the case of film, similarly, it is possible to change a type crystalline structure to B type crystalline structure by carrying out the operation of stretching and heat treatment, and also possible to obtain a strong film by maintaining l,/l at a figure less than 1.3.

EXAMPLE 4 Three unstretched polyvinylidene fluoride mono-filaments were made from the resinous materials by the suspension polymerization shown in Table I. These unstretched monofilaments, which were extruded at 250C through an orifice of 0.5 mm D by a plungertype melt extruding apparatus and were wound up at the respective draft ratios, were stretched at 120C with a draw ratio of 3 times. These stretched monofilaments were thus subsequently heat-set for 1 hour at 150C with a 2 percent elongation so that the orientation might set well.

The intensity ratio [,ll, measured by the X-ray diffraction diagram and the tensile strength and elongation of the oriented polyvinylidene fluorides monofilaments of this invention made by the procedure described above, are shown in Table VII, in which the tensile strengths are all more than 5.0 g/D and are excellent compared with the known commercial polyvinylidene filament.

EXAMPLE 5 The oriented monofilaments shown in Table VI] were again stretched at 170C with a draw ratio of percent and annealed for 1 hour under these conditions. Their intensity ratios and tensile properties are shown in Table VIII.

(Table VII) (Table VIII) I ll and Tensile Properties of Secondary Stretched Polyvinylidene Fluorides Monofilaments of This Invention A polyvinylidene fluoride film was made by the meltextrusion of 1; inh 0.92 through a slot orifice, and was wound up at 20 m/min. This was stretched with aa draw ratio of 250 percent at C while passing between two nip rolls. The thickness of this oriented film was 0.02 min. The tensile strength and the elongation of this oriented film were 35 lcg/mm and 35 percent, respectively, and the intensity ratio I,/I was 1/1.

What we claim is:

l. A shaped article of polyvinylidene fluoride having improved heat-resistance, mechanical stability, and dimensional stability, said shaped article having been prepared by polymerizing vinylidene fluoride at a temperature between 0 and 30C in a water medium in the presence of a catalyst selected from the group consisting of l a dialkyl peroxydicarbonate represented by the following general formula R-O-C-O-O-C-O-R wherein R is a primary alkyl group having 1-4 carbon atoms, or a secondary alkyl group having 3-6 carbon atoms, and

2. a dialkyl peroxy carbonate M1, and Tensile Properties of Various Oriented Polyvinylidene Fluorides Monofilaments of This Invention R-O-C-O-O-R' and 190C, a crystallization temperature of from 135 to 146C, and an inherent viscosity of from 0.4 to 1.20; and melt extruding said polymer at a temperature of about 250C and above to produce a pre-formed article of a film or fiber and stretching the pre-formed article at a temperature between and C and at a draw ratio of at least 150 percent to form a film or fiber having an intensity ratio of at most 1.3.

2. A shaped article according to claim I which is in fibrous form.

3. A shaped article according to claim 1 which is in the form of a film. 

1. A SHAPED ARTICLE OF THE POLYVINYLIDENE FLUORIDE HAVING IMPROVED HEAT-RESISTANCE, MECHANICAL STABILITY, AND DIMENSIONAL STABILITY, SAID SHAPED ARTICLE HAVING BEEN PREPARED BY POLYMERIZING VINYLIDENE FLUORIDE AT A TEMPERATURE BETWEEN 0* AND 30*C IN A WATER MEDIUM IN THE PRESENCE OF A CATALYST SELECTED FROM THE GROUP CONSISTING OF
 1. A DIALKYL PEROXYDICARBONATE REPRESENTED BY THE FOLLOWING GENERAL FORMULA
 2. A DIALKYL PEROXY CARBONATE
 2. a dialkyl peroxy carbonate
 2. A shaped article according to claim 1 which is in fibrous form.
 3. A shaped article according to claim 1 which is in the form of a film. 